Search

The analytical quality program of soil fertility laboratories that adopt the Embrapa methods (PAQLF) is a voluntary national sample-exchange program. PAQLF is managed by Embrapa Solos (National Soil Research Center), and actually is comprised of 82 Brazilian soil fertility laboratories that use P and K extraction with Mehlich-1 solution; Al, Ca, and Mg with KCl solution; soil pH in water; and total organic C by colorimetric or Walkley–Black methods. The quality of soil-test results is evaluated by true values taken as mean (accuracy) following removal of outliners by up to three interactions until CV falls below 20%, and by sample with three replications (precision). Inaccuracy and Imprecision Index are calculated for all laboratories and a ranking is established by an Excellence Index. Yearly the best ranked laboratories are indicated and qualified to use the Quality Control Seal. The objective of this research was to evaluate the performance in regard to accuracy and precision, characterize soil-testing...

Soil solution chemistry is a powerful tool for studying many aspects of soil science. Consequently, isolation and chemical analysis of the soil solution are essential procedures in soil chemistry studies. Among several isolation techniques, centrifugation appears most promising as a method of extracting the soil solution in the laboratory. However, some operational conditions must be defined. The present work reports the influence of the centrifugation time (30 and 60 min) and speed (560, 2,260, and 5,080 g) on the observed composition of the soil solution of four samples from two typical and representative Brazilian Oxisols. The concentrations of {\rm{ NH _{4} ^{ + } }, } Ca, Mg, Al, Na, K, Mn, Fe, Zn, Cl−, {\rm{ NO _{3} ^{ - } }, } {\rm{ SO _{4} ^{2 - } }, } and F− varied significantly with the centrifugation speed but not with time. Charge balance calculations for the evaluation of the electrochemical neutrality showed that an extraction time of 1 h at a speed of 2,260 g should be recommended for furth...

Cesium-137 (137Cs) soil-to-plant transfer factors obtained in an accidentally contaminated Oxisol in Goiânia and another Oxisol experimentally contaminated show that these soils present higher transfer of 137Cs from soil to plants than previously observed in temperate climates. These differences were discussed in the light of the pedology and geochemical partitioning. Some tropical soil characteristics, such as acidity, low availability of nutritive elements and low content of 2:1 clay type may account for the high mobility for 137Cs even after a long period after contamination. Results of sequential extraction showed that most of the 137Cs is bound to soil oxides.

Thirty-two soil samples from different locations of the Rio de Janeiro State, Brazil, were studied in order to evaluate the amount of aluminum (Al) obtained by three extractants (1 M KCl, 1 M NH4OAc, 0.5 M CuCl2) and by the extraction of humic and fulvic acids (0.5 M NaOH, following purification). The results were discussed in relation to statistical correlations with soil organic matter content and soil pH (water). In general, the displacement of Al followed the order: CuCl2 > NH4OAc > KCl > humus extraction. The greater amounts of Al extracted by CuCl2 were attributed mainly to Al from soil organic matter.

Considering the increasing need for reliable soil carbon (C) and nitrogen (N) determinations, 19 Brazilian soil samples were selected to compare the results of two methods (a) a modified dichromate wet digestion and Kjeldahl that has been in use by Embrapa in most of Brazilian soil surveys (Embrapa's method), and (b) an automated technique based on dry combustion (Perkin-Elmer 2.400 Series II–CHN Mode). Considering that the last method is very much influenced by sample size, two weights were tested (10 and 100 mg). The influence of two particle sizes for both methods (crushed and sieved to pass a 0.177-mm mesh) was also tested. A simple linear regression with the confidence limits for the intercept and slope were used to compare methods. Precision was evaluated by the coefficient of variation (C.V.). The results showed that simple crushing is inadequate for performance analysis by dry combustion mainly for small samples (10 mg), where the precision is also low (19.77% for N and 9.41% for C). The dry combu...